Increasing crime rates have led to growing demand for security and alarm systems. Traditional security systems use a variety of sensors for detecting intrusions into a secured area. They include, for example magnetic sensors, infra-red (IR) sensors, pressure pads and break sensors etc. IR sensors have limited use in security systems since an intruder must actually enter a building, before his entry is detected. Furthermore, rapid temperature changes can sometimes trigger a false alarm response from an IR sensor. Similarly, in order to provide adequate protection, IR sensors must be fitted to all the entry and exit points in a building; and all the sensors coupled to a central control panel. Thus, considerable costs are incurred in purchasing and fitting IR sensors; and connecting all the sensors to the central control panel. Furthermore, the wiring associated with these connections can often be aesthetically unpleasing.
In the case of magnetic sensors, these sensors must be fitted to all doors and windows in a building and be connected to a central control panel. Thus, magnetic sensors are subject to similar cost and aesthetic disadvantages to the IR sensors. Pressure pad sensors are typically only fitted to main entry and exit points within a building, thus these sensors have limited use, as an intruder must actually enter a building to activate the sensors. Similarly, pressure pad sensors must be connected to a central control panel. In the case of vibration sensors, the performance of these sensors can be affected by the presence of birds, traffic, the ambient moisture levels in a building, etc. Furthermore, in order to provide adequate protection, vibration sensors must be fitted to all of the windows in a building; and connected to a central control panel.
Whilst it is recognised that for complete protection of the perimeter of a building, it is necessary to fit sensors to all of the doors and windows in the building, in practice standard security systems typically only employ magnetic sensors fitted to entrance doorways and infra-red sensors fitted at key positions in the building.